A detailed laboratory study was performed to assess the use of carbon steel sacrificial anodes to galvanically protect UNS N04400 nickel alloy heat exchanger tubes in sea water applications. Several parameters were investigated: the potential-time relationsship of uncoupled and coupled steel-N04400, the current-time relationsship of the coupled alloys, the effect of two sacrificial anode system, the effect of water path length, and the effect of new and used N04400 alloy tubes. The present results demonstrate that the galvanic potential obtained under all test conditions was more negative than both the protection potential and the pitting potential values obtained for N04400 alloy in similar sea water conditions. The minimum galvanic potential recorded for the N04400 alloy (-310 mV(SCE)) was more negative than the protection potential (-60 mV(SCE)) and the pitting potential (+100 mV(SCE)). Under the testing conditions decribed, the application of sacrificial cathodic protection to N04400 heat exchanger tubes has been shown to prevent pitting corrosion, and thus can be expected to prolong tube service life. The current distribution along the length of the N04400 heat exchanger tube was inversely proportional to the distance along the tube. Increase in condenser tube length beyond 5 m significantly reduced the current throwing power, although the potential remained more negative than the protection potential value.
Effectiveness of cathodic protection of UNS N04400 heat exchanger tubes for sea water service
Wirksamkeit des kathodischen Schutzes von Wärmeübertragerrohren aus UNS N04400 für Meerwasser
British Corrosion Journal ; 30 , 4 ; 312-316
1995
5 Seiten, 9 Bilder, 1 Tabelle, 11 Quellen
Aufsatz (Zeitschrift)
Englisch
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